1. Field of the Invention
The present invention relates to a laser-decomposable resin composition, more specifically, a composition which can be engraved by a laser and satisfies both high decomposability and high stability, and a pattern-forming material using the composition.
2. Description of the Related Art
The decomposable resin and decomposable resin composition are a material such that the resin decomposes in response to an external factor such as thermal factor, mechanical factor, photochemical factor, radiation chemical factor and chemical factor, and are widely known. Changes caused by decomposition of the resin, that is, changes in the form (liquefaction, vaporization) between before and after decomposition of the resin or composition and changes in the nature or property such as molecular weight, hardness, viscoelasticity, glass transition temperature (Tg), solubility and adhesive property, are utilized and these resins or compositions are being used in various fields.
Examples of the decomposable resin and decomposable resin composition include a biodegradable plastic (e.g., polylactic acid) for decreasing the environmental effect of plastic materials, and a sustained-release material for gradually releasing a preparation, a fragrance or the like, which is used, for example, in the fields of medical treatments, cosmetics and life science. These are, however, a material which gradually decomposes in oxygen, light, enzyme, living body, soil or the like under a natural environment, but are not a material which stably maintains the initial state and abruptly brings about a great change in the nature by the effect of external stimulation.
In order to ensure a recycling property or simplify the waste treatment, there have been developed, for example, a resin which decomposes, or an adhesive which decreases in the adhesive property, by the effect of light or heat. It is also known to form a porous material by mixing a decomposable resin with ceramic, carbon fiber or the like and removing the decomposable resin through firing. However, these are a technique of treating and processing the material as a whole but not a technique of forming a necessary pattern only in a necessary portion. Furthermore, the decomposition treatment requires a large energy.
As for utilization in the image formation, there is known, for example, a technique of satisfying both storage stability as a toner and image fixing property by using a toner containing a thermally decomposable resin and utilizing changes in the nature due to heat at the fixing under heating. Here, however, the resin itself is not satisfactorily responsive to pattern-like stimulation.
As regards the pattern-forming material, for example, a photoresist of which pattern formation is performed by subjecting a composition containing a photoacid generator and an acid-decomposable resin to pattern-like exposure and, if desired, heat treatment to cause pattern-like decomposition of the resin and developing the resist film, is widely known as a so-called chemical amplification-type resist. Both storage stability and pattern-forming property of this composition are satisfied in a practical level, but a development process under satisfactorily controlled processing conditions is indispensable for the pattern formation and although applicable to a thin film, this composition can be hardly applied to pattern formation of a thick film, for example, in several tens of μm or more.
Furthermore, a method of forming an image by utilizing a step of imagewise irradiating laser light to partially remove (ablate) a thin film is known (see, JP-A-10-119436 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). However, examples described for the compound employed as a thermally decomposable resin are merely a normal general-purpose resin such as polyester, polycarbonate and polyurethane, and the film thickness is approximately from 1 to 2 μm at most. There is also known a case using a compound of which thermal decomposability is specified (see, JP-A-10-244751). However, even in this case, the film thickness is approximately from 1 to 2 μm at most.
As regards the mask material for use in paste printing or the like on a printed wiring board, a mask for forming a pattern of approximately from 100 to 200 μm by utilizing a photodecomposable sheet, and a production method thereof are disclosed (see, JP-A-8-258442). However, this patent publication is silent on specific compounds, and a controlled development processing is indispensable, because the pattern is formed by adjusting the degree of exposure and development.
On the other hand, as regards the technique of forming a pattern in a thick film by a simple processing, for example, pattern formation by laser processing is known, where a substrate itself is removed, deformed or discolored by the imagewise irradiation of laser light. For example, a laser marker is utilized for entering information such as lot number in products (e.g., videotape, home electric appliance) comprising various substrates. In this case, however, a normal resin or the like is directly used as the substrate itself.
In the pattern formation by laser processing, it is demanded that a laser-engraved part (trough) is swiftly formed. For this purpose, a laser-decomposable pattern-forming material having high sensitivity is necessary.
Particularly, in the case of a flexographic printing plate precursor of laser direct-drawing type (a so-called laser engravable flexographic printing plate), easy engravability by laser light (engraving sensitivity) governs the plate-making speed and therefore, a laser-engravable flexographic printing plate using a laser-decomposable resin composition having high sensitivity is demanded.
On the other hand, an imine bond is easily hydrolyzed in the presence of an acid catalyst. It is known that by utilizing this property, a polymer containing an imine bond is hydrolyzed by an acid and reduced in the molecular weight (see, JP-A-2003-73470 and H. Kanazawa, et al., Macromolecules, 39, 138-144 (2006)). Also, as for the composition of which depolymerization reaction proceeds under the action of a catalytic active species generated due to heat, there are known a depolymerization reaction by an acid generated from an acid generator (see, Y. Konno, et al., Polymer J., 36, 531-537 (2004) and JP-A-2003-119281), and depolymerization using a photoacid generator of polyphthalaldehyde (see, H. Ito et al., J. Photopolym. Sci. Technol., 3, 219-233 (1990)). In these publications, a depolymerization reaction or a resist composition is disclosed, but in a high-sensitivity system, occurrence of a decomposition reaction during production or storage of the composition can be hardly suppressed. Accordingly, a highly sensitive, highly stable composition is demanded.